The present invention concerns a roll for guiding web type material, specifically paper or cardboard which loops around the roll across part of its circumference, with a shell featuring a multitude of bores. A portion of the bores is covered by a covering device contained in the interior of the roll, while another portion can be subjected to suction from the interior of the roll.
Prior art rolls are known, for example, from German Patent Publication 14 74 973, German Patent Publication 28 12 099, German Patent Document 27 20 871, European Patent Document 01 18 384 and U.S. Pat. No. 3,869,095, respectively. On such rolls, only part of the roll shell is covered by the web. In the absence of specific design provisions, air is of necessity sucked through the bores in the uncovered area of the roll shell. This arrangement is undesirable and results in a loss of power. On the rolls according to the four references cited above, such design provisions have been made, for instance, in the form of suction segments in order to limit the intake space to the sector of the roll that is looped by the web. However, such design provisions require considerable construction expense.
Attempts have been made toward keeping the number and the cross-section of the bores as small as possible, so that the retention of the web on the roll is assured. An example may be found in German Patent Document No. 29 20 707. However, this is only a compromise and not an optimum solution.
This roll serves the function of a support roll in a dual support roll winder. In such a machine, during exchange of the reel for a new core, the roll is at standstill and subjected to suction in order to hold a new web leader looped on the roll shell until the core has been placed in the winder bed. The web leader previously has been formed by a severing operation. Since only part of the roll shell is covered by the web, leakage air passes of necessity through the uncovered bores during the suction operation. In the prior known roll, therefore, the number and cross section of the bores are kept at a minimum in order to avoid over-dimensioning the suction device that ensures the adherence of the web to the roll. The device for evacuating the interior of the roll is turned off during the winding operation.
During the winding operation, air is entrained by the moving web and also by the roll shell. The air trapped in the gore between the roll shell and the web can partly enter the roll through the bores contained in the roll shell and can escape through the bores of the shell area that is not covered by the web. But the number of bores in the roll shell and their size is not sufficient for that purpose, especially when operating at high winding speeds and with air-impermeable webs, for instance of coated paper. Therefore, air bubbles occur between the roll shell and the web or the web floats on the roll because its contact with the roll shell has been extensively eliminated. To remedy this shortcoming, which affects the quality of winding, it is also known to provide the roll shell with a helical grooving on its outer circumference, but this measure has only a limited effect.
Therefore, the problem underlying the invention is to improve a roll of the aforementioned type to the effect that the entire air volume trapped between the web and the roll shell is removed and the adherence of the web to the roll is achieved with little expense.